Refrigeration apparatus and method



Dec. 12, .1939. B. M. BUCHANAN REFRIGERATION APPARATUS AND METHOD Original Filed April 1, 1937 INVENTOR Lzsuz 3M.5UCH.ANAN.

WITNESSES: (v 72 Um. a" 23 ATTO NEY Patented Dec. 12, 1939 UNITED STATES PATENT OFFICE REFRIGERATION APPARATUS AND METHOD Leslie B. M. Buchanan, Springfield, Masa, assignor to Westinghouse Electric & Manufacturing Companin. East Pittsburgh, Pa., a corporation of Pennsylvania Application April 1, 1937, Serial No. 134,229 Renewed June 27, 1939 10 Claims.

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In order to control the flow of refrigerant between the high pressure side of a refrigerating system, of which the condenser is a part, and the low pressure side of the system, of which the evaporator is a part, a tube of considerable length and relatively small diameter, sometimes referred to as a capillary tube hasbeen heretofore utilized. One of the principal disadvantages of a capillary tube is that it depends primarily on the difference in pressure between the ends thereof for regulating the flow of refrigerant. It is, therefore, apparent that in a refrigerating system, for example, of the type wherein the condenser is air-cooled and the evaporator is subjected to varying heat loads, as in the usual domestic refrigerator, the pressure drop across the tube varies considerably, with the result that the amount of refrigerant liquid passed by the tube changes. For example, if the capillary tube is designed to operate in a room temperature of 80 F. and in a refrigerator cabinet wherein the air is normally maintained at 45 R, an increase in condenser temperature with consequent increase in pressure will result in forcing too much liquid through the tube. Likewise, a decrease in cabinet air temperature with consequent decrease in evaporator temperature and a decrease in the amount of refrigerant pumped and condensed in the condenser will result in too much liquid being forced through the capillary tubes. In either case, eventually all the liquid condensed will have been forced through the capillary tube and gas will then be forced through the tube in considerable quantities. This results in a loss in efliciency, since the gas does not effect refrigeration in the ,evaporator but is merely circulated through the system without doing useful work.

If the temperature of the air surrounding the condenser decreases below 80 F., with consequent decrease in condensing temperature, the amount of refrigerant passed by the'tube decreases and liquid will back up into the condenser. This results in increased head pressures at a time when head pressure should be decreasing, with consequent loss in efliciency. The pulldown characteristics of the system, that is, the amount of time and work necessary to bring the cabinet down to the desired temperature, are also deleteriously affected because of starving of the evaporator. Furthermore, when the evaporator temperature has increased, less refrigerant is being supplied thereto at a time when more refrigerant should be applied thereto to compensate for the increased heat load.

On the other hand, ii. the temperature of the air surrounding the evaporator increases above 45 F., the refrigerant gas pumped by the compressor is denser with the result that more pounds of refrigerant are pumped per stroke of the compressor. This also results in liquid piling up in the condenser because the capillary tube will not pass the increased amount of liquid which is being condensed since the-capillary tube is designed to operate at the 80 room, 45 cabinet temperature. This results in increased head pressure above the head pressure which should prevail because of the increased suction pressure. There .is consequently a loss in efliciency for this reason. Furthermore, the evaporator is starved and the "pull-down characteristics of the system are therefore deleteriously effected.

It is, therefore, an object of my invention to improve the operation of a capillary tube flow restrictor for a refrigerating system. Y It is another object of my invention to pass liquid refrigerant as it condensed to the evaporator of a refrigerating system utilizing a capillary tube flow restrictor.

It is still a further object of my invention to vary the flow restricting effect of a'capillary tube flow restrictor by abstracting heat therefrom in response to changes in condensing pressure and/or evaporator pressure, and furthermore, to accomplish this result by utilizing the refrigerant in the system for abstracting said heat.

It is another object of my invention to materially improve the efficiency of a refrigerating system utilizing a capillary tube, and an improved construction and method of operation for such a system.

It is a further object of my invention to vary the flow restricting effect of a capillary tube progressively and in. proportion to changes in pressure in the condenser and the evaporator of the refrigerating system, and to accomplish this result by a novel device which is of extremely simple and inexpensive construction.

These and other objects are effected by my invention as will be apparent from the following description and claims taken in connection with the accompanying drawing, forming a part of this application, in which:

Fig. l of the drawing illustrates diagrammatically a refrigerating system and control thereto provide for embodying my invention with the storage tank enlarged for the sake of clarity; and

Fig. 2 is a diagrammatic illustration of the evaporator and storage tank utilized in my invention and illustrates the relative size and position of these parts.

Referring specifically to the drawing for a detailed description of my invention, numeral I designates a compressor which is driven by an electric motor 2 through a coupling 3. Refrigerant compressed in the compressor I is conveyed to a condenser 4' through a conduit 5, wherein refrigerant is condensed, assisted by the cooling action of ambient air forced over the condenser by a motor driven fan B. Condensed refrigerant is then conveyed, in a manner more fully described hereinafter, to an evaporator I which is disposed within a storage chamber 8 of a heat insulated refrigerator cabinet 9. The evaporator I is connected with the suction of the compressor I ,through a conduit II, whereby vaporization of refrigerant is effected in the evaporator I with resulting cooling of the evaporator and the air in the storage chamber 8..

Refrigerant liquid is first conveyed to a refrigerated shelf 1a and then through a conduit I tothe evaporator proper.

The motor 2 is energized from a line L1, L2, in response to opening and closing of contacts I2, which contacts are operated by a bellows I3. The bellows I3 is connected by a conduit I4 to a bulb I5 which is in intimate thermal contact with the evaporator I. The bellows I3, conduit I4 and bulb I5 are filled with an expansible fluid so that the bellows I3- expands and contracts to close and open the contacts I2 in response to the temperature of the evaporator 1, whereby the motor and compressor are operated in response to evaporator temperatures. A spring I6 opposes the force exerted by the bellows and is'provided with a screw I1 for adjusting the force exerted by the spring so that the temperatures of the evaporator I at which the motor 2 is energized and deenergized may be-varied at the will of the user, and the temperature of the air in the storage chamber 8 may be maintained within desired limits.

Refrigerant liquid leaving the condenser 4 first enters a tube 20 of relatively small bore and of considerable length, sometimes called a capillary tube". The first portion of the capillary tube, designated at I8, is in heat exchange relation with the suction conduit II, whereby the efliciency of the system is improved by sub-cooling the condensed liquid and by utilizing the refrigerating effect of the refrigerant vapor and any refrigerant liquid in the suction conduit II. The second portion of the capillary tube, designated at I9, is preferably coiled and is disposed within an insulated tank 2|, into which the open end 22 of the capillary tube 20 discharges. The space between the coils of the capillary tube portion I9 is widened at the bottom so that changes in level in the tank 2I will be properly reflected in the abstraction of heat from the capillary tube. A tube 23 offering slight restriction to the flow of refrigerant, but not as much restriction as the capillary tube 20, connects the bottom of the tank 2| with the evaporator 1.

Operation The rate of flow of liquid refrigerant through a capillary tube is effected by several factors, for example, the length and bore of the tube, and the amount of gas entering or forming in the tube. The amount of gas forming or entering the capillary tube changes the restricting effect thereof because the restricting effect per unit of weight to the flow of gas through a capillary tube is considerably greater than the restricting effect per unit of weight to the flow of liquid. Since the length and bore of the tube are fixed for average operating conditions, and are not readily variable, the rate of flow of liquid through the tube may be varied by changing the amount of gas entering the tube or forming therein. For this purpose, in accordance with my invention, the capillary tube is disposed in heat exchange relation with a variable quantity of cold vaporizing refrigerant in order. to abstract varying amounts of heat from the refrigerant passing through the capillary tube in response to changes in pressures in the evaporator and the condenser. A similar system is 'described and claimed in a copending application of Carl F. Alsing, Serial No. 134,231, filed April 1, 1937 for Refrigeration apparatus and method.

In accordance with the present invention, the restriction to the flow of refrigerant through the capillary tube is progressively varied in proportion to changes in pressures in the condenser and the evaporator.

Assume that the contacts I2 are closed and that the compressor I is operating. Also assume that the outside air being forced over the condenser l is at 80 F. and the temperature of the air in the storage compartment is at 45 F. Liquid refrigerant from the condenser passes through the capillary tube 20' and enters the tank 2 I, but all of the refrigerant entering the tank does not immediately pass through the evaporator 1 due to the slight restriction of the tube 23. Liquid refrigerant. therefore, approximately half fills the tank 2| to the level shown at 24. The liquid refrigerant in the tank 2| is substantially at the pressure and the temperature of the evaporator because the refrigerant is evaporating and the vapor is passing through a a restricted tube 26 to the evaporator I. Since the tube 26 is slightly restricted, the evaporator pressure will, of course, be slightly lower than the pressure in the tank. It is necessary that the tube 26 be of substantially the same restriction as'the tube 23 to prevent liquid refrigerant from passing through the tube The liquid in the tank 2I is therefore colder than the refrigerant liquid in the capillary tube 20 and the liquid in the tank, therefore, cools the liquid in the portion I8 of the capillary tube. Such cooling tends to condense some of the refrigerant gas in the capillary tube and sub-cools the liquid therein so that it does not expand as rapidly as it reaches the open end 22 of the capillary tube 20. At the condition assumed, namely 80 air and 45 cabinet temperatures, a restriction to flow by the capillary tube is such that the head pressure is at a satisfactory low value and liquid is flowing from the tube 23 at such a rate that the level in the tank 2I is maintained as shown at 24. Any refrigerant vaporized in the tank 2I is conveyed to the conduit 26 and eventually to the compressor I through the evaporator I.

The flow through the restricted tube 23 is a function of the pressure difference across the tube, which is the difference between the sum of the liquid head and the gas pressure in .the tank 2I (hydrostatic pressure) at the inlet of the tube 23 compared with the pressure of the evaporator I at the outlet of the tube 23. The flow through the tube 23 for a constant pressure difference across the ends thereof is substantially the same at all times. By means of this invention, the

pressure difference across the tube 23 will be the same at all times for a given suction pressure and therefore a given rate of discharge of refrigerant liquid from the capillary tube. This is accomplished by changing the head of the liquid in the tank 2| or the gas pressure therein so that the fiow through the tube 23 will eventually be equal to the flow of liquid through the capillary tube. During the short intervals of time when the liquid level in the tank 2| is changing, it is obvious that the flow through the tube 23 will not be the same as the flow through the capillary tube 20. The pressure difference across the tube 23 will also be the same at all times for given discharge pressures because the head of the liquid in the tank 2| or the gas pressure therein will be changed so that the flow through the tube 23 will equal the fiow of liquid through the capillary tube except during the short intervals of time'wh'en the liquid level in the tank 2| is changing.

In other words, the invention operatestoprovide a substantially constant amount of liquid in both the condenser and the evaporator of a. re-

irigerating system utilizing a capillary tube, re-

discharge pressure which results in lower volu-.

metric efficiency of the compressor and secondly there is more heat in the liquid which is condensed and supplied to the capillary tube 20. The increase in the heat of the liquid in the capillary tube causes more of the incoming l quid to the tank 2| to be vaporized to cool the remaining liquid to the suction pressure prevailing in the tank with the result that the pressure of refrigerant in the tank 2| increases and temporarily forces more liquid through the slightly restricted tube 23 so that the level of refrigerant in the tank 2! drops to the level shown at 21. This increases the restricting effect on the fiow of liquid through the capillary tube 20, because morega's is formed in the capillary tube. The increased restriction to the fiow of refrigerant through the capillary tube prevents gas from ent ring the capillary tube from the condenser 4 because the condenser pressure slightly increases and refrigerant is liquefied more readily at the higher pressure with very little change in temperature. As heretofore noted, normally gas would be passed through the capillary tube with resulting loss inefficiency of the refrigerating system. Although the discharge pressure is slightly increased over normal, the loss because of the increased discharge pressure is more than offset by the gain attained in preventing gas from passing through the capillary tube results in less heat in the liquid in the capillary tube. Less of the incoming refrigerant to the tank 2| therefore is vaporized in order to cool the remaining liquid to the suction pressure .prevailing in the tank. The pressure in the tank therefore decreases and temporarily forces less liquid through the restricted tube 23 so that the level in the tank 2| will rise to the level shown at 25. Since more of the capillary tube 20 is immersed in the cold liquid refrigerant in the tank 2|, the restrictive effect on the flow of liquid through the capillary tube 20 is decreased. Normally, with decrease in discharge pressure as stated hereinbefore since the capillary tube is des gned to operate at a predetermined discharge pressure, refrigerant liquid will back up into the condenser. However, by my invention, the decrease in restriction to flow through the capillaryv tube allows the same fiow through the tube as at the conditions for which it is designed when the discharge pressure of the condenser decreases and the condenser therefore does not fill up with liquid. The increase in head forces the slightly increased amount of refrigerant pumped through tube 23 after the fiow stabilizes. The discharge pressure of the machine is thereby maintained at a desirable low value corresponding to the value at which it should be maintained for the lower ambient temperature and the machine therefore operates efllciently at the lower discharge pressure.

Assume now that the suction pressure increases because of a setting of the control device to a higher temperature or because of an increased heat load in the refrigerator cabinet. The first result is that more refrigerant is pumped by the compressor than was pumped before and the condensing pressure rises somewhat so that more liquid is condensed. This condition in an ordinary capillary tube machine would result in liquid rising in the condenser and increasing the discharge pressure beyond a desirable value in the same manner that decreasing condensing pressure would tend to fill up the condenser. However,

with my invention, the increased discharge presv within desirable limits which will of course be.

slightly higher than the discharge pressure before because of the increased suction pressure. The flow through the restricted tube 23 therefore increases because ofthe slightly increased head of the liquid at the level 25. The result w ll be that the amount of refrigerant which is being condensed will be passed to the evaporator except for the slight amount which increases the level in the tank 2|.

Assume now that the suction pressure decreases and the. discharge pressure remains constant. This results in less refrigerant being pumped by the compressor and a slightly lower condensing pressure both of which result in less liquid being condensed. Without my invention, thisv would result in all the liquid passing through the capillary tube 20 until gas would pass therethrough and lower the efiiciency of the system as explained hereinbefore. However, by utilizing my invention, the decreased discharge pressure forces less liquid through the capillary tube, the lower amount of liquid being equal to the decrease in liquid pumped. This causes the level in the tank 2! to fall to the level 21 and increases the resistance to flow through the capillary tube so that the condensing pressure is slightly increased and liquid is maintained at the entrance of the capillary tube which prevents gas from entering the capillary tube. In other words, the same effect is obtained as with increasing discharge pressure. The flow through the tube 23 then decreases because of the decreased head of the liquid in the chamber 2| and the flow through the capillary tube 20, and the restricted'tube 23 substantially equals the amount of liquid which is condensed except for the slight increase in liquid passed through the tube 23 due to the lowering of the level of refrigerant in the tank 2|.

It is of course obvious that the suction and discharge pressures may both change together or they may change separately as explained above. However, under all conditions, by utilizing my invention the proper amounts of refrigerant will be maintained in the condenser and in the evaporator and the capillary tube has its restriction so varied that it will pass substantially the same amount of refrigerant which is condensed under all conditions.

From the foregoing it will be apparent that I have provided refrigeration apparatusl and a method of operating the same wherein a capillary tube is utilized to control the flow of refrigerant between the condenser andthe evaporator of the system and wherein the restriction offered by the capillary tube is progressively varied in proportion to changes in the pressures in the high pressure and the lower pressure sides of the system.

I have shown an air cooled compressor refrigerating system herein, but it is obvious that the invention is not limited to either air cooling, or to compression refrigerating systems, but is applicable to the control of the flow of refrigerant between the high pressure and the low pressure portions of any type of refrigeration apparatus which embodies different pressure zones.

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof, and I desire,

, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What I claim is:

1. In refrigeration apparatus, the combination of an evaporator, a condenser, meansv for circulating refrigerant to said condenser for liquefaction therein and then to said evaporator for vaporization and to abstract heat therefrom, a capillary tube flow restrictor disposed between the condenser and the evaporator, and means for increasing or decreasing the restrictive. effect on the flow of refrigerant through said tube, said last means comprising a chamber into which said capillary tube discharges, said chamber surrounding said tube and normally containing a body of refrigerant liquid partially immersing said tube, said chamber having a restricted communication for vaporized refrigerant with said evaporator .so that refrigerant liquid vaporizes therein and cools the portion of the capillary tube which is immersed, and means for effecting a rise and fall of the level of the body of refrigerant in said chamber in response to chanses in pressure in said condenser and evaporator, whereby more or less of said capillary tube is immersed and cooled by said body of liquid and the flow therethrough is increased or decreased.

2. In refrigeration apparatus, the combination of an evaporator, a condenser, means for circulating refrigerant to said condenser for liquefaction therein' and then to said evaporator for vaporization and to abstract heat therefrom, a flow restricting device of relatively small bore and considerable length disposed between the condenser and the evaporator, and means for increasing or decreasing the restrictive effect on the flow of refrigerant through said device, said last means comprising a chamber normally containing liquid refrigerant disposed in heat exchange relation'with said device and being in communication with said evaporator so that re- -frigerant liquid in said chamber vaporizes therein and cools the flow restricting device, and means for varying the amount of liquid refrigerant in said chamber in response to pressure changes in said condenser and evaporator, whereby the heat abstracted from said device is increased or decreased.

3. The method of operating a refrigerating system having a condenser and an evaporator maintained at different, varying pressures and a capillary tube flow restrictor for regulating the flow of refrigerant from the condenser to the evaporator, which method comprises immersing a portion of the capillary tube in refrigerant liquid, evaporating some of theliquid to cool said tube and effecting an increase and decrease in the amount of the tube immersed in said refrigerant liquid in response to changes in pressure in said evaporator and the condenser to abstract more or less heat from said capillary tube and respectively decrease or increase the restricting effect of the capillary tube on the flow of liquid refrigerant from the condenser to the evaporator.

4. In refrigeration apparatus, the combination of an evaporator, a condenser, means for circulating refrigerant to said condenser for liquefaction therein and then to said evaporator for vaporization and to abstract heat therefrom, a capillary tube flow restrictor disposed between the condenser and the evaporator, and means for increasing or decreasing the restrictive effect on the flow of refrigerant through said capillary tube, said last means comprising a chamber into which said capillary tube dischargessaid cham ber surrounding'said tube and normally containing a body of refrigerant liquid partially immersing said tube, said chamber having a restricted communication for conveying vaporized refrigerant to said evaporator so that refrigerant liquid vaporizes therein and cools the 'portion of the capillary tube which is immersed, and means for effecting a rise and fall of the level of the body of refrigerant in said chamber in response to changes in pressure in said condenser and evaporator, whereby more or less of said capillary tube is immersed and cooled by said body of liquid and the flow therethrough is increased or decreased, said last means including a restricted tube connecting said chamber beiow the level of refrigerant therein with said evaporator, the flow of refrigerant through said last restricted tube being responsive to the hydrostatic pressure of the liquid in said tank.

5. The method of operating a refrigerating system having a condenser and an evaporator maintained at different varying pressures and a capillary tube flow restrictor for regulating the flow of refrigerant from the condenser to the evaporator, which method comprises immersing 5 a portion of the capillary tube in refrigerant liquid, evaporating some of the liquid to cool said tube and effecting an increase in the amount of the tube immersed in said refrigerant liquid in response to increase in suction pressure in the evaporator to abstract more heat from the capillary tube and decrease the restrictive efiect of the capillary tube on the flow of liquid refrigerant.

6. The method of operating a refrigerating system having a condenser and an evaporator maintained at different varying pressures and a capillary tube flow restrictor for regulating the flow of refrigerant from the condenser to the evaporator which method comprises immersing a portion of the capillary tube in refrigerant liquid, evaporating some of the liquid to cool said tube and effecting an increase in the amount of the tube immersed in said refrigerant liquid in response to decrease in condensing pressure to abstract more heat from said capillary tube and 85 decrease the restrictive effect on the capillary tube to the flow of liquid refrigerant.

7. The method of operating a refrigerating system having a condenser and an evaporator maintained at diflerent varying pressures and a 80 capillary tube flow restrictor for regulating the flow of refrigerant from the condenser to the evaporator which method comprises immersing a portion of the capillary tube in refrigerant liquid, evaporating some of the liquid to cool 85 said tube and efiecting a decrease in the amount of the tube immersed in said refrigerant liquid in response to a decrease in suction pressure of the evaporator toabstract less heat from the capillary tube and increase the restrictive effect of the capillary tube on the flow of liquid capillary tube flow restrictor for regulating theflow of refrigerant from the condenser to the evaporator which method comprises immersing a portion of the capillary tube in refrigerant liquid, evaporating some of the liquid. to cool said tube and effecting a decrease in the amount of the tube immersed in said refrigerant liquid in 5 response to increase in condensing pressure to abstract less heat from the capillary tube and increase the restrictive effect of the capillary tube' on the flow of liquid refrigerant.

9. In refrigerating apparatus, the combination in of an evaporator, a condenser, means for pumping refrigerant vapor from the evaporator to the condenser for liquefaction therein, and means for conducting the refrigerant liquid from the condenser to the evaporator and restricting the flow 15 of said refrigerant liquid substantially proportionately to the temperature difierence between the condenser and the evaporator, said lastnamed means comprising a chamber and a flow restricting device of relatively small bore and a0 considerable length discharging liquid refrigerant from the condenser into said chamber, said chamber being adapted to vaporize liquid refrigerant and discharge both liquid and vaporized re- 1 frigerant into said evaporator, and said flow re- 88 stricting device being in heat exchange relationship with the refrigerant in said chamber.

10. In refrigerating apparatus, the combination of an evaporator, a condenser, means for pumping refrigerant vapor from the evaporator to the condenser for liquefaction therein, and means for conducting the refrigerant liquidfrom the condenser to the evaporator and restricting the flow of said refrigerant liquid substantially proportionately to the pressure diflerence between the condenser and the evaporator, said last-named means comprising a chamber and a flow restricting device of relatively small bore and considerable length discharging liquid refrigerant from the condenser into said chamber, 40 said chamber being adapted to vaporize liquid refrigerant and discharge both liquid and vaporized refrigerant into said evaporator, and said flow restricting device being in heat exchange relationship with the refrigerant in said chamber. 5

' LESLIE B. M. BUCHANAN. 

